Turbine blade fastening



20 1940. c. R. SODERBERG 2,21 ,8 6

TURBINE BLADE FASTENING Filed March 31, 1939 INVENTOR Cam. RSooznaeaq ali al il 2| BY v 0V nabs F'm'Z F745 Has.

ATTORNEY Patented Aug. 20, 1940 UNITED STATES PATENT OFFICE 2,211,866 ITURBINE BLADE FASTENING Pennsylvania Application March 31,

4 Claims.

This invention relates to elastic fluid turbines and it has for anobject the provision of improved blading for apparatus of thischaracter.

Another object of the invention is the provision of blades of the T-roottype, the outer surfaces of whose lateral root lugs are relieved at thefront and back edges thereof to provide for a stronger root constructionand one in which the maximum stresses are substantially reduced.

These and other objects are effected by this invention as will beapparent from the following description and claims taken in connectionwith the accompanying drawing forming a part of this application, inwhich:

Fig. 1 is a fragmentary, longitudinal sectional view through two rows ofimpulse blading embodying the invention Fig. 2 is a transverse sectionalview taken along the line IIII of Fig. 1, looking in the direction ofthe arrows;

Fig. 3 is an enlarged fragmentary View of a portion of the structureshownin Fig. 2;

Figs. 4 and 5 are views similar to Fig. 3, showing two modifications ofthe structure thereof;

Fig. 6 is a stress diagram for the previously known form of T-rootblade, under tangential loading;

Fig. 7 is a stress diagram for a T-root blade made in accordance withthe present invention, under tangential loading; and,

Figs. 8 and 9 are stress diagrams corresponding to those of Figs. 6 and7, respectively, but showing stresses under radial loading rather thanunder tangential loading.

Figs. 6, '7, 8, and 9 correspond to sections taken on the line XX ofFig. l.

Referring now to the drawing, there is shown a rotor l 0 carrying tworows of blades l i, adapted to have rotary movement imparted thereto bya motive fiuid supplied through the nozzles I2 and the reversing bladesl3 carried by the stator l4.

Each blade ll includes a root part l6 comprised by a spacing portion H,a head portion I8 and a neck portion l9 joining the spacing and headportions.

The head portion 18 has lugs 21 extending laterally of the neck portionand having outer surfaces 22 adapted to engage the inner surfaces 24 ofthe usual rotor blade groove projections or ribs 25.

Heretofore, the outer blade groove rib-engaging surfaces 22 of the lugs2! have extended for the full width of the latter from the front to theback. With this construction, the application of 1939, Serial N0.265,113

centrifugal or tangential forces to the blade has resulted in a maximumconcentration of stresses in the neck portion of the blade root adjacentthe edges thereof (Figs. 6 and 8), and localized overstressing of bladeroots in this manner subjects the blades to greater likelihood offailure than would be the case if the overstressing could be avoided.

To reduce the aforesaid maximum stresses, a shown in Figs. 3, 4, and 5,the side edges of the outer surfaces 22 are relieved, as at 21, wherebythe maximum stresses occur at points spaced inwardly (Figs. 7 and 9)with reference to the front and back surfaces of the root, the surfacesof the root corresponding to front and back surfaces of the blade beingdesignated in like manner. Inward transference of the location ofmaximum stresses results in substantial reduction in the maximum valuethereof, for example, in the ratio of 9 to 5, and in consequence, theblade roots are stronger and less likely to crack at the edges.

The lug top surfaces 22 may be relieved at the front and back edges inany suitable manner. In Fig. 3, the top surface is chamfered, at 28,adjacent to the edges; in Fig. 4, relief at the front and back edges isafforded by having the top surface 22 formed on a radius which is lessthan the radius of the inner circumferential surface 24 of the grooverib 25, each surface 22 so provided being curved with respect to an axisparallel to the rotor axis; and in Fig. 5, the top surfaces 22 arerelieved by rounding them to a relatively small radius, as shown at 30.

Fig. 6 shows diagrammatically the stresses present in the neck portionwhen the blade is subjected to tangential forces or loading, where theouter surface 22 of the lug 2| engages the inner rib surface 25 for itsfull width from the front to the back, the maximum stresses occurring inthe neck portion of the root at the front and back edges of the lugs.

Fig. '7 shows a corresponding stress diagram for blade roots constructedin accordance with the present invention, this construction resulting inre-location of the maximum stresses at points disposed inwardly of theside edges of the blade root neck. As indicated, this results inreducing the maximum stresses to about of their original value.

Figs. 8 and 9 show the stresses present in the previously known bladesand in blades constructed in accordance with the invention,respectively, when subjected to centrifugal or radial loadings. The samegeneral results are obtained under these conditions, the maximumstresses being moved inwardly and reduced to about of their originalvalues.

Throughout the specification and claims all terms and expressionsrelating to location or direction refer to such location or directionwith respect to the axis of rotation of the blade-carrying member orrotor l0.

While I have shown my invention in several forms, it will be obvious tothose skilled in the art that it is not so limited, but is susceptibleof various other changes and modifications without departing from thespirit thereof, and I desire, therefore, that only such limitationsshall be placed thereupon as are imposed by the prior art or as arespecifically set forth in the appended claims.

What I claim is:

1. A turbine blade comprised by blade and root parts and said root partincluding a spacing portion, a head portion, and a neck portion joiningthe spacing and head portions and having less width than the latter,whereby the head portion has lugs extending laterally from the neckportion for underhanging relation with respect to blade groove ribs andthe top surfaces of the lugs being relieved at their front and backedges.

2. A structure as specified in claim 1, wherein the lugs are relieved atthe front and back edges of their outer surfaces by chamfers.

3. A structure as specified in claim 1, wherein the lugs are relieved atthe front and back edges of their outer surfaces by rounding of saidedges.

4. A structure as specified in claim 1, wherein the outer surfaces ofthe lugs are formed on a radius which is less than the radius of thesurfaces with which they are adapted to engage, said radii being aboutaxes parallel to the axis of rotation of the blade-carrying member.

CARL R. SODERBERG.

